A conventional vehicle air conditioning unit, such as that disclosed in, for example, JP-A-10-138742, includes actuators for rotationally driving various kinds of doors, such as, for example, an air mix door, through output shafts. Control circuits respectively detect the present position of each output shaft and control each actuator based on the detected position to drive each output shaft to a target stop position. The vehicle air conditioning unit also includes an electrical control unit which communicates with each control circuit to transmit a target stop position for each actuator.
As mentioned above, each control circuit of the vehicle air conditioning device drives the output shaft to the target stop position based on its present position. Accordingly, each control circuit is required to recognize the accurate present position of the output shaft in order to drive the output shaft to the target stop position at high precision.
However, electrical noise resulting from, for example, electromagnetic waves may cause the control circuit to malfunction and erroneously reset the memory or garble data when information on the present position is received. The present position recognized by the control circuit then becomes deviated from the actual present position.
That is, the present position recognized by the control circuit is made abnormal by the effect of the electrical noise. When the control circuit controls the actuator based upon an abnormal present position, the control circuit drives the output shaft to a position out of the original target stop position. This may induce lock or the like and thus cause the actuator to be uncontrollable.